Nearly one in every five sexually active teen girls say they’ve been hit, slapped or beaten up by a date in the past year, an alarming new study reveals.

Just as disturbing, the girls who are abused often engage in risky sexual practices – like sleeping with numerous partners over a short period of time.

The results have prompted the Harvard School of Public Health, which conducted the study, to urge educators to include dating violence in sexual-health and pregnancy-prevention classes.

“Dating violence is prevalent among [American] adolescent girls – especially those reporting having had sexual intercourse,” said Dr. Jay Silverman, who spearheaded the research.

“[And] adolescent girls intentionally hurt by a date in the previous year are more likely to experience sexual-health risks – including [increased] vulnerability to HIV and other sexually transmitted infections, and to have been pregnant.”

Harvard quizzed 6,864 female high-school students and found of the 43 percent who said they’ve had sex, 18 percent said they’d been physically hurt in the past year.

The study also found girls who reported incidents of dating violence were twice as likely to have had three or more sexual partners in the past three months.

And they were also 50 percent more likely to have started having sex before age 15 or to have used alcohol or drugs the last time they had sex.

For those who said they’d never had sex, only 4 percent confessed to being abused.

In addition, girls who reported physical abuse from a date were less likely than other girls to have used a condom the last time they had sex.

Whether it’s the physical abuse that leads to the riskier behavior or another reason is unclear and must be studied further, the report said.

While girls in the study did not identify the abuser’s sex, they are believed to be mostly men because recent research found that only a small number of adolescent girls report same-sex contact.

The study asks for additional studies to determine exactly why some teen boys hit their dates and what can be done to prevent it.

It also recommends establishing more places that girls who experience dating violence can go to for help.

The research is published in the August issue of the journal Pediatrics.

Dating from hell

* 1 in every 5 sexually active teenage girls has been smacked around by a date

* Those reporting dating violence were twice as likely to have had 3 or more partners in the past 3 months.

* Half were likely to have had sex before age 15 or to have used alcohol or drugs when they had sex.

* More likely to be exposed to sexually transmitted diseases like HIV, as well as becoming pregnant.

* Of the girls who’d never had sex, only 4 percent were dating violence victims.